The present disclosure relates to a red phosphor, and a method of production thereof, and to white light sources, illuminating devices, and liquid crystal display devices using a red phosphor.
A white light source formed of a light-emitting diode is used as the backlight of illuminating devices and liquid crystal display devices. A known example of such a white light source is one in which a cerium-containing yttrium aluminum garnet (hereinafter, “YAG:Ce”) phosphor is disposed on the emission side of a blue-emitting diode (hereinafter, “blue LED”).
As another example, those including green and red sulfide phosphors disposed on the emission side of a blue LED are known (see, for example, Patent Document 1). Further, there has been proposed a configuration in which a fluorescent material prepared as a solid solution of elements such as Mn and Eu in a CaAlSiN3 crystal is disposed on the emission side of a blue-purple- or blue-glowing LED with another fluorescent material at a predetermined proportion (see, for example, Patent Document 2).
Patent Document 1: JP-A-2002-60747
Patent Document 2: Japanese Patent No. 3931239
However, because the white light source including the YAG:Ce phosphor disposed on the emission side of the blue LED lacks a red component in the YAG:Ce phosphor emission spectrum, the white light appears bluish, and the color gamut is narrow. Thus, it is difficult to produce pure white illumination with illuminating devices that use such a white light source. Further, display with desirable color reproducibility is difficult to achieve with a liquid crystal display device that uses such a white light source as the backlight.
In the white light source including the green and red sulfide phosphors disposed on the emission side of the blue LED, luminance degrades overtime because the sulfide red phosphor undergoes hydrolysis. It is therefore difficult to produce high-quality illumination or display of non-degrading luminance with an illuminating device or a liquid crystal display device that uses such a white light source.
The white light source using the fluorescent material prepared as a solid solution of elements such as Mn and Eu in a CaAlSiN3 crystal is laborious, because it uses and mixes two kinds of fluorescent material.
It is therefore desired to provide a red phosphor of strong luminous intensity and high luminance, a method of production thereof, a white light source and an illuminating device that use the red phosphor and produce pure white illumination, and a liquid crystal display device that has desirable color reproducibility.